System and method for suppressing DC link voltage buildup due to generator armature reaction

A method of preventing a build-up of voltage on a DC link connected to an exciter field winding of a generator as a result of an unbalanced short-circuit fault at an output of the generator, the method comprising:

• monitoring each phase of output voltage generated by the generator;
• calculating an average voltage value based on the monitored output voltage;
• applying a control loop that detects and modifies a voltage ripple component detected within the average voltage value to generate a compensated signal;
• and
• applying the compensated signal to the exciter field winding to counteract an armature reaction voltage ripple generated in response to the unbalanced short-circuit fault.

A synchronous generator comprising:

• an input for receiving direct current (DC) voltage from a DC source;
• an exciter field winding;
• exciter armature windings mounted on a rotatable shaft that is magnetically coupled to the exciter field winding such that the DC current provided to the exciter field winding induces an alternating current (AC) voltage in the exciter armature windings;
• a rotating rectifier mounted on the rotatable shaft and operably connected to the exciter armature windings to convert the AC voltage generated on the exciter armature windings to a DC voltage;
• a main field winding mounted on the rotatable shaft and operably connected to receive the DC voltage generated by the rotating rectifier;
• main armature windings magnetically coupled to the main field winding such that the DC voltage provided to the main field winding induces an AC output voltage in the main armature windings;
• a controller having a first input operably connected to monitor the AC output voltage generated by the main armature windings and to apply a control loop to the monitored output voltage that detects and modifies the monitored output voltage to generate a compensated signal;
• wherein the controller employs the compensated signal to control the excitation provided to the exciter field winding to minimize armature reaction ripple voltage caused by unbalanced short-circuit conditions.

A computer readable storage medium encoded with a machine-readable computer program code for generating thereof a compensated signal in response to a detected unbalanced fault condition, the computer readable storage medium including instructions for causing a controller to implement a method comprising:

• acquiring input from one or more sensors positioned to monitor output voltage and output current of a generator;
• detecting an unbalanced fault condition based on the monitored output current;
• calculating an average mean squared voltage signal based on the monitored output voltage;
• detecting a voltage ripple signal in the average mean squared voltage signal;
• applying a phase shift to the voltage ripple signal;
• applying a gain to the phase-shifted voltage ripple signal to generate the compensated signal;
• and
• providing as an output to a current loop controller for generating a desired current on an exciter field winding the compensated signal.